Research On Method Of Pre-warning And Prediction For Spewing And Ground Surface Movements In Shield Construction

With the advancement of urbanization in China,shortage of urban space resources has increased,the development of underground space has been taken seriously,metro projects have been launched in major cities,and shield method is currently the main method used in urban subway tunnel construction.As the interaction between shield method and surrounding water and soil environment is a very complex system problem,safety accidents have occurred constantly such as spewing and the movements of ground surface,which ring the alarm bell for engineers.It is of great practical significance to study the methods of spewing warning and ground surface movements predicting.This paper mainly adopts theoretical derivation and numerical simulation to study the warning of spewing and the prediction of the ground surface movements in shield construction on the basis of previous studies,improving and supplementing the current prediction methods.Aiming at the spewing problem of screw conveyor,the main contents of this paper are as follows:(1)Based on the basic laws of groundwater seepage,establishing a seepage model considering the stratum parameters,shield geometry conditions,as well as additional thrust on the front of the excavation face,of muck in screw conveyor.and combining with the critical conditions of the spewing to establish the spewing prediction model of screw conveyor and give the pre-warning index.The influence of various parameters on spewing is studied through the orthogonal experiment method basing on the pre warning index.(2)The influencing law of the additional thrust at the excavation face on the excess pore water pressure of stratum is analyzed by theoretical derivation and numerical model,the prediction method of spewing is improved in this study.The influencing law of muck permeability coefficient on the seepage of groundwater in screw conveyor is analyzed,and the pre-warning index is verified by the comparison of theoretical derivation and numerical model.Aiming at the prediction method of the deformation of ground surface during shield tunneling,the following researches are carried out in this paper:(1)The basic law of stratum movement induced by shield tunneling is analyzed in the previous part of the research,based on Mindlin solution and modification on the corrected formula of image method,the basic mechanics principles and discrete summation are used to derive the prediction formula of the ground surface movements in shield tunneling considering the tunneling angle;(2)Through the establishment of three-dimensional numerical models with different shield pitch angles and the comparison and verification with the calculation result of theoretical derivation formula,the influencing law of the shield pitch angle and the tunnel axis inclination angle on the ground surface movements is analyzed;(3)Taking the shield tunnel of Wuhan Metro line No.6 as an example,a threedimensional model of the tunnel axis with a certain inclination angle is established,the existing prediction method,corrected formula derived in this research and numerical simulation method are used to calculate the ground surface movements of the Wuhan shield construction,comparatively verifying the accuracy of method in this study and the rationality of considering the construction angle as a factor which influence the ground surface movements.